| ||In the spring of 2007, Alberta beekeepers found higher than average winterkill losses in over-wintered bee colonies. To determine the extent of winterkill, Alberta Agriculture and Food conducted a survey of 112 beekeepers with 400 or more colonies.
Survey results show that 30 percent of Alberta bees were killed in the 2006 / 2007 winter. This reported winterkill is twice the long-term average in Alberta but is in line with this year’s Canadian average (29 percent). The survey also reveals that 15 percent of the surviving colonies were weak with less than 3 frames covered with bees. The survivorship and production of these weak colonies in 2007 is questionable.
The winterkill plus weak colonies percentage was lowest in region 1 (southern Alberta), followed by central regions 2, 3 and 4, and region 5 (Peace River area) was the highest. Overall in the province, 50 percent of the beekeepers reported losing about half of their productive hives in 2007 due to winterkill and weak colonies.
The responses in this survey indicate that disappearance or starvation were not major factors in the higher overwinter losses in Alberta. The data also reveals that loss rates cannot be attributed the Colony Collapse Disorder (CCD) currently in the United States.
Over-winter losses in Alberta during 2006 / 07 may be attributed to a combination of several potential causes:
The potential causes for overwinter losses outlined in this survey are in agreement with reports from other provincial apicultural specialists.
- The unusual weather conditions during the 2006 bee season encouraged the retention of summer bees and reduced the production of winter bees.
- The late arrival of spring in 2007 prolonged winter stress and delayed availability of spring forage.
- Varroa mites unexpectedly developed resistance to applied miticides. Consequently, mite populations were higher than normal in bee colonies and damaged winter bees.
- The earIy onset of winter made it difficult to treat varroa with alternative products to protect winter bees.
- The late treatments also increased the stress on hives, making them more vulnerable to winterkill factors.
- In spring 2007, beekeepers reported higher than normal incidence of Nosema-like symptoms. The percentage infection with Nosema-like symptoms was positively correlated with winterkill and winterkill plus weak colonies. Though beekeepers feed medicated sugar syrup in the fall to control Nosema, the chemotherapy did not work well in some cases. The failure of treatment is under investigation.
- Viruses and other pathogens were often present as a secondary infection and this added stress to over-wintering colonies.
|For a complete copy of this report download the .pdf file above.|| |